Utilization of a power take-off (PTO) shaft on equipment such as a tractor or the like to power associated agricultural implements is commonly known in the industry. Typically, the PTO shaft is coupled to an output shaft which is selectively driven through mechanical gearing at standardized speeds of either 540 rpm or 1000 rpm. The PTO shaft is configured for connection to an implement which is also designed to be operated at either 540 rpm or 1000 rpm.
In order to avoid connecting to implements for operation at the wrong speed, the power take-off shaft is typically configured with a standard 13/8 inch diameter connection having six splines for connecting to 540 rpm implements, and/or 21-splines for connecting to 1000 rpm implements. Alternatively, some PTO shafts are configured with a standard 13/4 inch diameter connection having 20 splines for connecting to 1000 rpm implements with similarly configured coupling mechanisms.
Thus, in order to accommodate the requirements of a particular implement, it is necessary to provide a power take-off assembly which allows quick and easy conversion to the desired PTO shaft configuration and associated speed of operation.
Various mechanisms have been employed for converting to a desired PTO shaft configuration and associated speed of operation. Some prior art devices utilize interchangeable PTO shafts having either six tooth or 21 tooth splines for connection to an associated implement. Other devices utilize a single reversible PTO shaft having six tooth and 20 tooth spline ends extending in opposite axial directions. In either configuration, the desired PTO shaft speed is typically determined by the configuration of the PTO shaft inserted into the output shaft. When reversible PTO shafts are used, the outer end portion is adapted for engagement with the implement for the selected speed, while the configuration of the inner end portion positions a shifting mechanism against the force of a spring to selectively engage the proper speed drive gear. For example, if it is desired to operate at a speed of 540 rpm, the PTO shaft is inserted so that the outer end portion is a six-spline connection, and the inner end portion has a configuration which positions the shifting mechanism to selectively engage the 540 rpm gear.
The PTO shafts in these devices are often maintained in place by a flanged locking mechanism arranged externally of the output shaft to which the PTO shaft is coupled. One disadvantage of the PTO shafts with connecting flanges is that it tends to be tedious and time consuming to connect the flange to the output shaft by bolts or the like.
Other known PTO shafts are maintained in place by an internal snap-ring configured to engage an interior bore of the output shaft. Because of the high force required to compress the snap-ring for installation, special tools such as pliers are usually required to interchange the PTO shaft, which tends to be cumbersome and time consuming. The snap-ring installation is made even more difficult when installing the PTO shaft in the 1000 rpm position. To perform this installation, an operator must push the PTO shaft to overcome the high axial force of the spring-loaded shifting mechanism, and at the same time install the snap-ring. In addition, the location of the snap-ring may add to these difficulties because it is exposed to debris, especially in the dirt and mud-filled environment of a farming field, thus making it difficult to properly use the tools. Moreover, the snap-ring connection may not be secure enough to adequately retain the PTO shaft during high speed operation. As will be appreciated by those skilled in the art, the PTO shaft is subjected to axial forces during operation of the agricultural implement. Accordingly, the snap-rings used to releasably fasten the PTO shaft in place may have insufficient strength to retain the PTO shaft in place.
It therefore remains desirable to provide a simple locking mechanism for quickly and securely connecting the PTO shaft to the output shaft in a desired orientation without the use of tools.